FR2727045A1 - Turn lock for drive shaft of cutting blade of free=cutting unit - Google Patents

Abstract

The turn lock includes a locking element (11) fixed to the drive shaft, with at least one aperture for a locking bolt (23). The bolt can move axially and is sprung by a spring (30). The locking bolt is disengaged by an operating element (41).The locking element is alongside the locking bolt, and has a setting cam (40) projecting into the lifting path of the locking bolt. The cam is fitted in the casing (2) of the unit (1) in at least one setting position which can be present so that the locking bolt is held in the disengaged position against the force of the spring.

Description

Locking device in rotation for a tool. bridged
turning. a machine tool
The present invention relates to a rotation blocking device for the drive shaft of a rotary tool of a machine tool, in particular of a cutting tool of a brush cutter or the like, with a safety element connected fixed in rotation to the drive shaft and which has a stop opening for engaging a blocking pin, which is mounted so as to be able to slide axially in the casing of the machine tool and is biased by a spring to move in the direction of the stop opening, and with an actuating member for passing the locking pin from an engagement position in the stop opening to a position out of grip.

 Thanks to American patent 4690252 there is known a rotation blocking device of the kind defined above and in which the blocking pin is supported, by means of a compression spring, on an actuating element. To block the tool, the actuating element must be made to slide, against the force of the spring, relative to the blocking pin and be fixed. This requires a special tool or a special handle for the actuating element. After the actuating element slides relative to the blocking pin, the latter is urged by the compression spring to move in the direction of the engagement position so that during rotation of the tool the locking pin may fall into a stop opening of the safety element fixedly connected in rotation to the shaft so that the drive shaft is locked.

 This rotation blocking device is made up of several moving parts with respect to each other, which during work in an environment laden with dirt can lead to operational incidents due to dirt having penetrated the device.

 Thanks to American patent no. 3899852 there is known a device for blocking in rotation, the blocking pin of which is biased by a compression spring to pass into the out-of-engagement position. To block the drive shaft the pin blocking must be pushed, against the force of the spring, into a stop opening of the safety element and be retained in this opening. This rotation blocking device has a simple construction but poses problems in inevitable deposits of dirt in the region of the locking pin, because if the deposits of dirt are so large that the compression spring is no longer able to push the locking pin back into the disengaged position, then the machine tool itself must be opened to remove the locking pin despite the dirt.

 The object of the present invention is to improve a device for locking in rotation of the kind defined above so that even when used in an environment heavily loaded with dirt, safe and incident-free operation remains assured.

 This object is achieved, as regards a device for locking in rotation for the drive shaft of a rotary tool of a machine tool, in particular of a cutting tool of a brush cutter or the like, with a safety element fixedly connected in rotation to the drive shaft and which has a stop opening for engaging a blocking pin, which is mounted so as to be able to slide axially in the casing of the machine tool and is urged, by a spring, to move in the direction of the stop opening, and with an actuating element for passing the locking pin from an engagement position in the stopping opening in a position out of engagement, according to the invention, by the fact that the actuating element is mounted next to the locking pin and has an operating cam projecting in the movement path of the locking pin and which in the envelope of the mac hine-tool can be fixed to the casing in at least one preset adjustment position and retains, in this adjustment position, the blocking pin, against the force of the spring, in the out-of-engagement position.

 The blocking pin subjected to the action of the spring in the engagement position is mounted, so as to be able to slide axially, in the casing of the machine tool, an actuating element disposed next to the pin of blocking projecting with an operating cam in the movement path of the blocking pin. Thus the locking pin is raised, against the force of the spring, by the operating cam from the engagement position to the out of engagement position, so that the operating cam is secured to the casing in this adjustment position and can in this way retain the blocking pin, against the force of the spring, in the out-of-engagement position. When the blocking pin becomes more difficult to move the machine tool retains its good state of service because the blocking pin has come out of the stop opening by means of the actuating force and not by a spring subjected to an initial tension. If the operating cam can advantageously actuate the locking pin also in the direction of the engaging position, then the locking pin can be made to slide axially in the casing bore which guides it and thus be kept in good condition working condition, without having to open the machine tool.

 Preferably, the operating cam is, in the adjustment position, fixed in friction connection to the casing of the machine tool, the actuating element for this purpose bearing in friction connection against a surface of the 'envelope. This can be ensured by the action of a spring so that the available friction connection is adjustable by the choice of the spring. The friction connection withstands, in the out-of-engagement position, the force of the spring acting on the locking pin.

 According to another characteristic of the invention, the friction connection between the operating cam and the casing of the machine tool becomes all the greater the greater the angle of rotation in the direction of the adjustment position.

 In the adjustment position, the operating cam is advantageously fixed to the casing of the machine tool in shape connection, in particular by engagement.

 The actuating element is produced in particular in the form of a rotary button which comprises a head disposed outside the casing and an interior part provided with the operating cam. The head of the rotary button has an outer annular surface which, disposed opposite an annular surface of the envelope, is retained by the spring, in friction connection, in contact with this latter surface, the actuating element taking support, preferably in friction connection, against a surface of the casing disposed opposite an annular flange, preferably external, of the head of the rotary button and, in particular, the head of the rotary button having a guide part which projects substantially adjusted in a cylindrical housing of the envelope.

 The operating cam is advantageously produced in the form of an involute tooth.

 Advantageously disposed between the cylindrical actuating element and the casing is a stop device by means of which the position out of engagement is advantageously locked so that the operating force of the spring urging the locking pin is retained .

 This stop device can be in the form of a blocking ball with an associated stop housing or, advantageously, a leaf spring fixedly connected to the envelope and which in the manner of a secant cut the circular path of the actuating element to be moved about an axis of rotation; the plane of the leaf spring can extend substantially parallel to the axis of rotation. To obtain a well-defined stopping position, the leaf spring rests with one side on an external flat, parallel to the axis of rotation, of the peripheral surface of the cylindrical actuating element. Preferably, the operating cam engages, in each adjustment position, in the axial bore of the casing which guides the locking pin. To this end, a rotary stop can be provided on the rotary button. associated, in the housing of the envelope, complementary stops integral with the envelope.

 To allow, in the case of blocking pins which are difficult to move, actuation by the operating cam both in the direction of the engagement position and in the direction of the out-of-engagement position, it is provided that the operating cam s engaging in a recess in the form of a peripheral groove in the blocking pin and preferably that the axial length of the recess in the blocking pin corresponds substantially to the stroke of the operating cam and either preferably, slightly less than this stroke. By applying an actuating force, the blocking pin can then be moved at least over an initial part of its path so that a blocking pin stuck in the axial bore can be released.

 The head of the rotary button can advantageously be made in the form of a nut, the surface of which (or key opening) corresponds to that of the tool tightening nut.

The invention is explained in more detail below, using an embodiment illustrated in the accompanying drawings in which
Figure i shows, in top view and partially in section, a cutting head of a brush cutter equipped with a rotation blocking device
Figure 2 is a sectional view along line II II of Figure 1
Figure 3 is a top view of a safety disc to be fixedly connected in rotation to the drive shaft of the cutting head
FIG. 4a is a side view, partially in section, of the cutting head, the rotation locking device being in the position without engagement
FIG. 5a represents, in an enlarged manner, the part shown partially in section in FIG. 4a
Figure 4b is a side view, partially in section, of the cutting head, the rotation locking device being in the released position
Figure 5b shows, on a larger scale, the part shown partially in section in Figure 4b
FIG. 4c is a side view, partially in section, of the cutting head, the rotation locking device being in the engagement position
FIG. 5c represents, in an enlarged manner, the part shown partially in section in FIG. 4c
Figure 6 is a partial sectional view of the rotation blocking device equipped with a stop device fixing the adjustment position
Figures 7a to 7d are partial sectional views of the rotation blocking device with a stop device, formed of a leaf spring, fixing two adjustment positions.

 The rotation blocking device for the drive shaft of a rotary tool of a machine tool is shown, in the embodiment, on the cutting head of a brush cutter.

 The cutting head 1 has a casing 2 in which is mounted a drive shaft 3 extending over the entire height of the casing 2. The drive shaft 3 is retained in the casing 2 by means of two rolling bearings 4 and 5, and in the region between the two rolling bearings 4 is mounted on the drive shaft 3 a bevel gear 6 which meshes with a bevel drive pinion which is not specially shown. The drive bevel gear is driven by a shaft arranged in a guide tube, which guide tube protrudes into a connection neck 7 (Figure 1) and is connected via a clamping sleeve 8 so fixed to the casing 2 of the cutting head 1.

The casing 2 is closed on the side of the tool 10 by a protective ring 9 which is produced, in section1 slightly in the form of a cap. In the protective ring 9 is fixed in rotation, on the drive shaft, 3 a safety element which in the example is produced in the form of a safety disc 11. As shown in FIG. 3, the disc safety li has on its inner periphery a grooved toothing 12 which engages, in shape connection, in a corresponding grooved toothing 13 of the drive shaft 3. The protective ring 9 in the form of a cap, receiving the disc safety 11, is closed by a protective disc 14, the edge 14a of the protective disc and the edge 9a of the protective ring overlapping axially. The slot s between the edges 9a and 14a is large enough for the protective disc 14 to rotate freely inside the protective ring 9; on the other hand, the slot s is small enough to largely prevent the entry of coarse dirt. The protective disc 14 can advantageously be fixedly connected to the safety disc 11.

 After the protective disc 14, a tool 10 is slipped onto the drive shaft 3, for example a sharp blade, which is then, by means of a tightening nut 16, axially tightened, by means of a pressure disc 15, sufficiently strong that the tool 10 is fixedly connected in rotation to the drive shaft 3. The clamping nut 16 is screwed onto a thread 17 at the free end of the 'drive shaft 3 in the clamping nut 16 is preferably placed a ring 18 of plastic material serving as protection against the risk of loss.

 In the casing 2 of the cutting head 1, a lateral lubrication opening 19 is formed which opens into the space between the rolling bearings 4, 5 and is closed in leaktight manner by a closing screw 20.

 In the safety disc 11 is provided a stop opening 21 for the engagement of the engagement section 22 (Figure 5a) of a locking pin 23. In order not to produce imbalance is provided, diametrically opposite each stop opening 21, a corresponding stop opening 21 of the same dimension. In the embodiment shown the safety disc 11 has four stop openings 21 (Figure 3).

 As is apparent from FIGS. 2 and 3, the safety disc has an outer edge 24 projecting in the direction of the casing 2 and which extends, to a large extent without play, up to the protective ring 9. On the diverted side of the envelope 2 there is disposed between the protective disc 14 and the safety disc 11 a protective plate 25 which corresponds substantially to the outside diameter of the safety disc 11. Thus the stop openings 21 extending up to at the edge 24 are covered, vis-à-vis the protective disc 14, by the protective plate 25. In this way the space between the protective plate 25, the edge 24 of the safety disc 11 and the protective ring 9 is in a largely protected against ingress of dirt.

 In the embodiment, the locking pin 23 extends approximately perpendicularly, preferably exactly perpendicular to the safety disc 11.

As shown in Figures 4a to 4c, the longitudinal axis 26 of the locking pin 23 therefore extends parallel to the axis of rotation 27 of the drive shaft 3. The locking pin 23 is mounted so able to slide axially in a casing bore, which casing bore 28 is preferably produced in the form of a blind hole 28. Between the bottom 29 of the blind bore 28 and the front side 30 of the dowel blocking 23, which faces the bottom 29, is mounted a spring 31 which in the embodiment shown is provided as a compression spring. Advantageously, it can also be provided with Belleville washers or other energy accumulators.

 The end of the locking pin 23 which is opposite to the front side 30 forms the engagement section 22, which is made for its engagement in a stop opening 21 of the safety disc 11. Preferably , the diameter of the engaging section 22 is less than that of the base body 33 of the locking pin 23. In particular, the diameter of engaging section 22 is slightly less than the width B, measured in the direction device, a stop opening 21 (FIG. 3).

 Between the engagement section 22 and the front side 30 of the locking pin 28, which is biased by the spring 31, there is formed in the base body 33 a splay, in particular a peripheral groove 32, of so as to form an actuating section 34 of the locking pin 23.

 In this recess, or peripheral groove, 32 engages an operating cam 40 of a rotary button 41, which is received, as shown in Figures 1 and Sa to 5c, in a cylindrical housing 35 of the envelope. The axis 36 of the cylindrical housing 35 of the envelope extends transversely to the axis 37 of the blind bore 28; the cylindrical housing 35 of the casing then cuts the blind bore 28 in the region of the actuating section 34, that is to say of the peripheral groove 32, of the locking pin 23. Under these conditions a plane radial of the cylindrical housing 35 of the envelope preferably extends exactly perpendicular to a radial plane of the blind bore 28.

 The rotary button 41 has a first part 43 disposed in the cylindrical housing 35 of the envelope and at one end of which follows a guide part 44 which engages in an adjusted manner, at the level of the open end. of the cylindrical casing housing 35 therein. The guide portion 44 follows a head 42, arranged outside the envelope, of the rotary button 41, which is, as shown in FIGS. 4a to 4c, produced in the form of a nut 45. the surface 45 (or overhang, or key opening) of the nut 45 corresponds in this case preferably to that of the tightening nut 16.

 The rotary button 41 is produced in the form of a hollow cylinder, the inside diameter of the head 42 being greater than the inside diameter of the inside part 43.

The inner annular shoulder 46 thus formed serves as a bearing surface for the peripheral edge of a washer
Belleville 47 which is preferably retained axially on the annular shoulder 46 by a screw 48. The screw 48 is screwed into a fixing dome 38 integral with the envelope and which engages in the interior part 43 of the rotary button 41 and protrudes slightly beyond the annular shoulder 46. The free end 39 of the fixing dome 38 has a reduced diameter and passes through the Belleville washer 47 so that the screw 48 can be fixedly tightened on the casing without lock the rotary button 41.

Due to the axial elastic force of the washer
Belleville 47 an outer annular flange 49 of the head 42 is pushed axially against an annular surface 50 of the casing 2. Between the annular flange 49 and the annular surface 50 a friction connection is established which dynamically prevents the movement of rotation of the rotary button 41. The fact that the annular flange 49 bears in friction connection on the annular surface 50 of the casing 2 also ensures the sealing of the cylindrical housing 35 of the casing against sap, dirt and the like ; advantageously, the superimposed annular surfaces are machined.

 The inner part 43 of the rotary button 41 carries on its periphery a radial operating cam 40 which, as shown in FIG. 1, preferably extends over the entire axial length of the part 43 located at: 'inside the envelope and follows axially from the guide portion 44. The operating cam 40 is produced in the manner of an involute toothing so that there is substantially only punctual contact of the operating cam 40 with a shoulder associated annular 40a of the recess, or peripheral groove, 32. Preferably, the annular shoulders 40a are chamfered over their entire radial height, so that jamming between the operating cam 40 and the locking pin 23 is avoided at for sure. The other annular shoulder, disposed opposite the annular shoulder 40a, of the recess 32 is preferably made in an identical manner.

 The rotational movement of the rotary button 41 is limited by a rotary stop 51 (FIG. 5a), which stop is, in the embodiment shown, roughly diametrically opposite the operating cam 40 on the outer periphery of the part interior 43. With the rotary stop 51 is associated, in the embodiment shown, in each of the two directions of rotation respectively a complementary stop 52 secured to the casing, so that the rotational movement of the rotary button 41 and, therefore, the reciprocating movement of the operating cam 40 is limited by construction. In addition, it is provided that the operating cam 40 protrudes in each possible adjustment position, that is to say over its entire travel, in the bore 28 of the casing. Consequently, the operating cam 40 engages, in each adjustment position, in the peripheral groove 32 so that entry of the operating cam 40 in contact with the annular shoulders of the peripheral groove 32 can occur at any time.

 FIGS. 4a and 5a show the position out of engagement of the locking pin 23. The operating cam 40 bears, preferably punctually, against the annular shoulder 40a of the peripheral groove 32.

Since the rotary button 41 is held by the spring, which is preferably made in the form of a Belleville washer 47, by means of the annular flange 49 in friction contact against the annular surface 50 of the casing , the operating cam 40 is, in this adjustment position, fixed to the casing. The force of the compressed coil spring 31 is retained, in friction connection, in the annular surface between the annular flange 49 and the annular surface 50 of the casing. This has the advantage that the median diameter of the annular flange 49 and therefore also of the annular surface 50 of the casing is approximately at the height of the point of application of the operating cam 40 on the annular shoulder 40a of the peripheral groove 32. By enlarging the annular flange 49 or the button 41 it is at any time possible, using a larger lever arm, to withstand even a greater spring force exerted on the locking pin 23 .

 I1 may be advantageous to ensure the position out of engagement of the locking pin 23, shown in Figure Sa, by form connection in the envelope 2. For this it can be formed in the region of the rotary stop 51 on the bottom of the cylindrical housing 35 of the envelope a bead or a step 55 behind which engages, in the out-of-engagement position of FIG. 5a, the rotary stop 51. I1 may also be advantageous to provide on the bottom of the recess 35 an elevation 70 preferably in the form of a partial ball on which the rotary button 41 slides against the force of the Belleville washer 47. Preferably, the elevation engages in a corresponding recess in the side front of the part 43 of the rotary button 41 so as to obtain an engagement.

This engagement is provided, in addition to the friction connection, as a means for sure preventing any untimely deactivation of the rotation blocking device.

 Another type of device preventing the rotation of the rotary button 41 is shown in FIG. 6. This device can be provided as a replacement or in addition to the subjection in rotation by friction link. For this it is arranged between the outer periphery of the inner part 43 and the inner periphery of the cylindrical housing 35 a stop device. The latter is constituted by an engaging ball 82 which, liable to being submerged, against the force of a stop spring 83, in a radial blind hole, engages with part of its periphery in a stop opening 80 or in a stop opening 81 formed in the wall of the cylindrical housing 35.In this case the ball 32 engages in a stop opening with less of a hemispherical cap so that during rotation of the rotary knob the engagement ball 82 is pushed back into the receiving hole against the force of the stop spring 83. In the representation of FIG. 6 the stop opening 80 is used for blocking the position out of engagement, while the stop opening 81 can also ensure the operating position of the rotary button, and therefore also of the operating cam 40.

 In the embodiment shown> the receiving hole, for the stop spring 83 and the engagement ball 82, is formed radially in the rotary stop 51 which is located between the complementary stops 52 integral with the casing. It may be advantageous to provide the locking device between the complementary stops 52 and the inner part 43 of the rotary button.

 FIG. 1 shows the arrangement of a blocking device between the bottom of the housing 35 and the front face, on the bottom side, of the internal part 43. Preferably, there is provided, as shown diagrammatically in FIG. front side in the peripheral direction, preferably at equal intervals, elevations 70 so as to prevent the rotary button, by sliding on the elevations 70, from tipping over. The arrangement of the elevations 70 on the bottom of the housing 35 also has the advantage that the annular flange 49 is raised slightly, by about 3 mm, from the annular surface 50 facing it and integral with the envelope, so that when passing from an adjustment position in contact with a first stop 52 to the other adjustment position in contact with the second stop 52 and conversely the friction connection is canceled and that consequently the rotary knob can be turned more easily.

 If, in order to replace the cutting tool 10, the latter or the drive shaft 3 must be blocked, then the nut 45 of the rotary button 41 is turned by means of the nut wrench which is also necessary for loosening the tightening nut. The head 2 of the rotary button 41 and the casing 2 respectively carry a radial nose 60; 61 which, as shown in FIGS. 4b and 5b, are in coincidence in the released position of the rotation blocking device. The user can then recognize that he has released the rotation blocking device. The locking pin 23 is pushed, under the action of the spring 31, against the safety disc 11, regardless of whether a stop opening 21 is coincident or not with the locking pin 23. In the 'exemplary embodiment shown, the engagement section taken 22 of the locking pin 23 is supported, according to Figures 4b and 5b, on the safety disc itself, because there is still no stop opening 21 coincidentally under the engagement section 22. To allow the rotary knob 41 to be brought without incident into the released position according to FIG. 4b, the axial length of the recess, that is to say the peripheral groove 32, is adapted to the length of the reciprocating movement, or stroke, of the operating cam 40. Preferably, the axial length is equal to the stroke or slightly greater than the latter.

 After the release of the rotation blocking device the user will put the nut wrench in place on the clamping nut 16 and, since the engagement section 22 of the blocking pin 23 has not yet been engaged, will rotate tool 10 and drive shaft 3 until a stop opening 21 is placed in coincidence under the engaging section 22. Under the action of spring 31, which even exerts in the engagement position according to Figures 4c and 5c still a spring effect, the locking pin will fall into the stop opening 21 so as to lock the drive shaft 3 in a fixed manner in rotation .The loosening force of the tightening nut 16 is deflected, via the safety disc 11, directly on the locking pin 23 and the casing 2 without the conical wheels of the transmission mechanism of the head of section 1 are subject to constraints. After replacing the tool, the rotary button 41 is returned to the position of FIG. 4a, which has the effect that the operating cam 40 lifts the locking pin 23 axially by pressing against the annular shoulder 40a of the peripheral groove 32, so that the engaging section 22 emerges from the stop opening 21 and the tool 10 is released to be driven by the drive shaft 3. In the out-of-engagement position shown in the FIGS. 4a and Sa the force of the spring 31 is retained in friction connection by the rotary button 41 and / or deflected, by a bead or heel 55, in shape connection in the envelope 2.

 The rotary button 41 may preferably be made of a sintered material, the rotary button 41 is made of plastic, in particular of a sintered plastic.

The locking pin 23, on the other hand, is preferably made of metal; it may be advantageous to make it out of plastic.

 To ensure, also in the engagement position, a reliable fixing of the compression spring on the front side 30 of the locking pin, a safety section 59 can be made on the locking pin engaging the spring black pudding.

 In the embodiment of Figures 7a to 7d there is provided a rotation locking device which in its basic design corresponds to that of Figures Sa to 5c.

The same reference numbers are used for the same constituent elements. The rotation blocking device of FIGS. 7a to 7d comprises a stop device which is essentially constituted by a leaf spring 90, which cooperates with flats 94 and 95 provided on the peripheral surface of the cylindrical part 43 of the rotary button 41 The ends 91, 92 of the leaf spring 90 are freely supported in pockets 89 of the casing 2, the leaf spring being arranged, in its extended state shown in FIGS. 7a, 7c and 7d, substantially parallel to the axis of rotation 36 of the rotary button 41.

In this extended state the leaf spring 90 is arranged, in its longitudinal extent, approximately parallel to the axis 37 of the bore 28 of the casing.

 In the extended state of the leaf spring 90, the latter bears, with its flat side 93 facing the rotary button 41, against a flat 95 (FIG. 7a) or 94 (FIGS. 7c, 7d).

In this extended state, the leaf spring 90 cuts the peripheral surface 96 of the cylindrical part 43, which surface constitutes the circular path of the actuating element, or rotary button, 41 to be rotated about the axis of rotation 36 This means that during a rotary movement of the rotary button 41 around the axis 36 the longitudinal edge 97 forces the leaf spring 90 to move away from the axis of rotation 36, as shown in FIG. 7b as an intermediate position. The flat 95 is followed by a second flat 94, the angle 98 included at the level of the common longitudinal edge 97 being less than 1800.

During a subsequent rotational movement of the rotary button 41 the longitudinal edge 97 moves towards one 91 of the ends of the leaf spring 90 so that this resumes its extended state elastically and is applied with its flat side 93 against the flat 94. The flat 95 is associated with the out-of-engagement position of Figure 7a, while the flat 94 is associated with the engagement position of Figure 7d. In order to surely exclude excessive rotation of the rotary button 41 beyond the engagement position or the out-of-engagement position, the stops 51 are provided which cooperate with complementary stops 52 integral with the envelope. are provided separately for the engaging position and the out of engagement position and are each located, in the peripheral direction, respectively between the cam 40 and the flat 94; 95 neighbor of the latter.

 The longitudinal edge 97 formed between the flats 94 and 95 constitutes a cam of the engagement device which cooperates with the leaf spring 90, so that to obtain the passage from the position out of engagement to the position of engagement taken, this cam must, by defeating the force of the leaf spring 90, be moved beyond the median plane 99 of the latter. In the median plane 99 is also arranged the axis of rotation 36 of the rotary button 41.

 In the representation of FIG. 7a, the locking pin 23 is retained in its position out of engagement against the force of the spring 31, the embodiment of the leaf spring 90 and of the longitudinal edge 97 produced at the manner of an engagement cam being such that the torque necessary for the rotation of the rotary button 41 is greater than the torque exerted on the cam 40 by the spring 31, subjected to an initial tension, of the locking pin 23. When the rotary button 41 is rotated, the leaf spring 90 deforms elastically, passing from the extended state to a convex state according to FIG. 7b, the free mounting of the ends 91 and 92 in the pockets 98 of the envelope being advantageous in this respect. As soon as the cam 40 releases the locking pin 23, the latter is pushed, under the action of the spring 31 subjected to an initial tension, in the direction of the safety disc 11. If there is no opening d stop 21 under the stretch of engagement 22, then the engagement section bears on the safety disk 11. The peripheral groove 32 has an axial length such that despite the fact that the locking pin 23 has not fallen into the stop opening the rotary button 41 can be brought into its stop position corresponding to the engagement position (FIG. 7d). In this engagement position the flat 94 is supported against the extended spring 90, and in this regard it may be advantageous to subject the leaf spring to a slight initial tension exerted towards the flat. This allows to obtain that in each stop position the leaf spring 90 takes support, under a pre-established spring tension, against the flats 94 and 95 defining the adjustment positions. By rotation of the safety disc 11 a stop opening 21 is brought into the region of the engagement section 22 until it falls into the stop opening 21; the locking pin 23 is then in its engagement position.

 To unlock the rotation locking device, the rotary button 41 is turned backwards, anti-clockwise so as to push the leaf spring 90 until the stop position in FIG. 7a is reached again. The locking pin 37 is now lifted out of the stop opening 21 of the safety disc 11 and is securely retained in this extended position.

Claims (12)

 1. Device for locking in rotation for the drive shaft of a rotary tool of a machine tool, in particular of a cutting tool of a brush cutter or the like, with a safety element (11) connected fixed in rotation = the drive shaft (3) and which has a stop opening (21) for engaging a locking pin (23), which is mounted so that it can slide axially in the casing (2) of the machine tool (1) and is biased by a spring (30) to move in the direction of the stop opening (21), and with an actuating element (41) for passing the locking pin (23) from an engagement position in the stop opening (21) to an out-of-engagement position, characterized in that the actuating member (41) is disposed next to the locking pin (23) and has an operating cam (40) projecting in the path of alternative movement of the locking pin (23) and which can, in the casing (2) of the machine tool (1), be fixed to the casing in at least one preset setting position and retains, in this setting position, the locking pin (23) in the out of engagement position against the force of the spring (30).  2. rotation blocking device according to claim 1, characterized in that in the adjustment position the operating cam (40) is fixed, in friction connection, to the casing (2) of the machine tool (1 ).  3. Device for locking in rotation according to claim 2, characterized in that the friction connection increases as the angle of rotation in the direction of the adjustment position increases.  4. A rotation blocking device according to any one of the preceding claims, characterized in that in the adjustment position the operating cam (40) is fixed in form connection, in particular by engagement, to the casing (2) of the machine tool (1).  5. A rotation blocking device according to any one of the preceding claims, characterized in that the actuating element (41, is produced in a cylindrical form as a rotary button and comprises a head (42) disposed at the exterior of the casing (2) and an interior part (43) provided with the operating cam (40), the actuating element (41) preferably taking support in friction connection on a surface (50) of the casing (2) and the casing surface (50) being opposite a preferably external annular flange (49) of the head (42) of the rotary button (41), and in that in particular the head (42) of the rotary button (41) has a guide portion (44), which extends substantially in an adjusted manner in a cylindrical housing (35) of the envelope (2), the rotary button (41) preferably being provided with a rotary stop (51) with which are associated, in the housing t35) of the envelope, stops additional (52) fixedly connected to the envelope.  6. A rotation locking device according to any one of the preceding claims, characterized in that the operating cam (40) is produced in the form of an involute tooth.  7. rotation blocking device according to any one of the preceding claims, characterized in that there is provided between the outer periphery of the inner part (43) and the inner periphery of the cylindrical housing (35) a stop device , in particular an engagement ball (82).  8. rotation blocking device according to claim 7, characterized in that the stop device is constituted by a leaf spring (90) fixedly connected to the casing and which cuts, in the manner of a secant, the circular path of the actuating element (41) to be rotated about an axis of rotation (36), the plane of the leaf spring (90) being substantially parallel to the axis of rotation (36 ).  9. rotation blocking device according to claim 8, characterized in that the leaf spring (90), in the substantially extended state, bears on an outer flat (94, 95), oarallel to the axis of rotation (36), also of cylindrical actuation (41), the actuating element (41) preferably having two external flats (94, 95) which meet at a certain angle (98) and are associated respectively with the engagement position and out of engagement position.  10. rotation blocking device according to any one of the preceding claims, characterized in that the operating cam (40) engages in a recess, produced in the form of a peripheral groove (32), of the dowel blocking (23), the axial length of the recess (32) in the blocking pin (23) corresponding substantially to the length of the reciprocating movement, or stroke, of the operating cam (40) and preferably being slightly less to this race.  11. A rotation blocking device according to any one of the preceding claims, characterized in that the operating cam (40) projects, in each adjustment position, into the axial bore (28) of the casing (2 ), which guides the locking pin (23).  12. A rotation blocking device according to any one of the preceding claims, characterized in that the head (42) of the rotary button (41) is produced in the form of a nut (45), the surface of which corresponds to that of the clamping nut (16) of the tool (10).